The use of chronic intracortical multielectrode arrays has become increasingly prevalent in neurophysiological experiments. However, it is not obvious whether neuronal signals obtained over multiple recording sessions come from the same or different neurons. Here, we develop a criterion to assess single-unit stability by measuring the similarity of 1) average spike waveforms and 2) interspike interval histograms (ISIHs). Neuronal activity was recorded from four Utah arrays implanted in primary motor and premotor cortices in three rhesus macaque monkeys during 10 recording sessions over a 15- to 17-day period. A unit was defined as stable through a given day if the stability criterion was satisfied on all recordings leading up to that day. We found that 57% of the original units were stable through 7 days, 43% were stable through 10 days, and 39% were stable through 15 days. Moreover, stable units were more likely to remain stable in subsequent recording sessions (i.e., 89% of the neurons that were stable through four sessions remained stable on the fifth). Using both waveform and ISIH data instead of just waveforms improved performance by reducing the number of false positives. We also demonstrate that this method can be used to track neurons across days, even during adaptation to a visuomotor rotation. Identifying a stable subset of neurons should allow the study of long-term learning effects across days and has practical implications for pooling of behavioral data across days and for increasing the effectiveness of brain-machine interfaces.

Studies of stimulus-secretion coupling in human beta-cells have been hampered by poor availability of tissue due to variability of the supply of cadaver pancreati and in the adequacy of enzymatic liberation of islets as well as by the shunting of isolates into transplant trials. Here we establish that aliquots of islets, several from high-quality but low-yield islet isolates (50,000-100,000 islets), cryopreserved and then thawed as needed, respond to glucose in a calcium- and metabolic-dependent fashion. Insulin secretion is modulated by blockers of voltage-dependent Na+ and Ca2+ channels, and paracrine hormones (glucagon and somatostatin) in manners indistinguishable from fresh tissue preparations. Using single-cell electrophysiological and electrochemical assays we demonstrate that single beta-cells from cryopreserved islets display (1) stimulus-depolarization coupling based on rapid closure of K+ (ATP) channels; (2) action potential electrogenesis with upstrokes based on voltage-dependent Na and Ca currents; and (3) Ca2+ entry-mediated depolarization-exocytosis coupling sustained over multiple bouts of stimulation and modulated by paracrine hormones. All of these features are indistinguishable from those seen in single cells from freshly harvested islets. These results support the utility of cryopreservation, even of low-yield but functional isolates, as a means of ensuring a steady source of repeatedly accessible tissue for research on normal and diabetic islets.

Mapping of cortical functions is critical for the best clinical care of patients undergoing epilepsy and tumor surgery, but also to better understand human brain function and connectivity. The purpose of this review is to explore existing and potential means of mapping higher cortical functions, including stimulation mapping, passive mapping, and connectivity analyses. We examine the history of mapping, differences between subdural and stereoelectroencephalographic approaches, and some risks and safety aspects, before examining different types of functional mapping. Much of this review explores the prospects for new mapping approaches to better understand other components of language, memory, spatial skills, executive, and socio-emotional functions. We also touch on brain-machine interfaces, philosophical aspects of aligning tasks to brain circuits, and the study of consciousness. We end by discussing multi-modal testing and virtual reality approaches to mapping higher cortical functions.

Recordings from chronically implanted multielectrode arrays have become prevalent in both neuroscience and neural engineering experiments. To date, however, the extent to which populations of single-units remain stable over long periods of time has not been well characterized. In this study, neural activity was recorded from a Utah multielectrode array implanted in the primary motor cortex of a rhesus macaque during 18 recording sessions spanning nine months. We found that 67% of the units were stable through the first 15 days, 31% of units were stable through 47 days, 21% of units were stable through 106 days, and 8% of units were stable over 9 months. Thus not only were units stable over a timescale of several months, but units stable over 2 months were more likely to remain stable in the next 2 months.

α-Latrotoxin (α-LT), a potent excitatory neurotoxin, increases spontaneous, as well as action potential-evoked, quantal release at nerve terminals and increases hormone release from excitable endocrine cells. We have investigated the effects of α-LT on single human, mouse and canine β-cells. In isolated and combined measurements, α-LT, at nanomolar concentrations, induces: (i) rises in cytosolic Ca 2+ , into the micromolar range, that are dependent on extracellular Ca 2+ ; (ii) large conductance non-selective cation channels; and (iii) Ca 2+ -dependent insulin granule exocytosis, measured as increases in membrane capacitance and quantal release of preloaded serotonin. Furthermore, at picomolar concentrations, α-LT potentiates depolarization-induced exocytosis often without evidence of inducing channel activity or increasing cytosolic Ca 2+ . These results strongly support the hypothesis that α-LT, after binding to specific receptors, has at least two complementary modes of action on excitable cells. (i) α-LT inserts into the plasma membrane to form Ca2+ permeable channels and promote Ca 2+ entry thereby triggering Ca 2+ -dependent exocytosis in unstimulated cells. (ii) At lower concentrations, where its channel forming activity is hardly evident, α-LT augments depolarization-evoked exocytosis probably by second messenger-induced enhancement of the efficiency of the vesicle recruitment or vesicle fusion machinery. We suggest that both modes of action enhance exocytosis from a newly described highly Ca 2+ -sensitive pool of insulin granules activated by global cytosolic Ca 2+concentrations in the range of ∼1 µM.